1. Field of the Invention
This invention is directed to wellbore drilling top drive systems; shaft seal systems for them; and methods of their use.
2. Description of Related Art
The prior art discloses a variety of top drive systems; for example, and not by way of limitation, the following U.S. patents present exemplary top drive systems and components thereof: U.S. Pat. Nos. 4,458,768; 4,807,890; 4,984,641; 5,433,279; 6,276,450; 4,813,493; 6,705,405; 4,800,968; 4,878,546; 4,872,577; 4,753,300; 6,007,105; 6,536,520; 6,679,333; 6,923,254—all these patents incorporated fully herein for all purposes.
Certain typical prior art top drive drilling systems have a derrick supporting a top drive which rotates tubulars, e.g., drill pipe. The top drive is supported from a travelling block beneath a crown block. A drawworks on a rig floor raises and lowers the top drive. The top drive moves on a guide track.
The main shafts of top drives have main shaft bearings which are critical to operation of the top drive and thus to the operation of the drilling rig. Contamination from moisture or leaking drilling fluid is a common cause of failure of main shaft bearings. Leaking drilling fluid can originate from leaks at a top drive's high pressure swivel seal above a top drive main bearing and gear housing. Leaking fluid can then flow down into the top drive bearings and gears.